1. Field of the Invention
The present invention relates to a rear-wheel steering device for a vehicle, which is designed to steer rear wheels by an actuator in operable association with the steering of front wheels by the operation of a steering wheel.
2. Description of the Related Art
A conventional rear-wheel steering device for a vehicle is known from, for example, Japanese Patent Application Laid-open No. 6-127409.
When an abnormality occurs in a control system for the actuator in the rear-wheel steering device for the vehicle, the vehicle steering is switched from a four-wheel steering state to a front-wheel steering state while a steering angle of the rear wheels is fixed, so that the vehicle may continue traveling without problem. In this case, if the steering angle of the rear wheels is small (e.g., 1° or less), the electric current supply to the actuator is cut off, while maintaining the small steering angle. If the steering angle of the rear wheels is large, the actuator is temporarily driven to return the steering angle of the rear wheels to zero, and thereafter the electric current supply to the actuator is cut off.
When the vehicle is traveling in the state in which the steering angle of the rear wheels is fixed as described above, if the steering angle of the rear wheels is changed due to a load from a road surface, the subsequent traveling of the vehicle may be hindered. Therefore, a worm gear is conventionally disposed in a path of transmission of a driving force from the actuator to the rear wheels so that the transmission of the driving force from the side of the rear wheels toward the actuator is inhibited during an abnormal operation, thereby preventing undesired changes in the steering angle of the rear wheels, while permitting the transmission of the driving force from the side of actuator towards the rear wheels during a normal operation.
However, it is difficult to inhibit the reverse transmission of the driving force from the side of the rear wheels toward the actuator only by means of the worm gear, and there is a possibility that the steering angle of the rear wheels is gradually changed due to an external force or the like, while the vehicle continues to travel.